CB2203 - CROP UPDATE 3 - 9th May 2022

Downy mildew in beans
There have been widespread reports of downy mildew in both winter and spring beans. Infection becomes obvious in late spring when conditions are humid, and plants can develop symptoms before flowering. The leaves develop characteristic pale patches on the upper surface and grey/ mauve mycelium develop on the underside of the leaves.

Infection starts from soil-borne oospores, which can remain viable for many years, and primary infection leads to an abundance of spores that are carried to surrounding plants by wind.

Downy mildew in winter beans

Infection is encouraged by cool, moist and overcast conditions, although not typically by rain. Humid conditions are required for secondary infection on the leaves and when temperatures average around 10°C. Recent conditions have been very suitable for downy mildew infections in beans. Although it is generally spring beans that suffer more damage from the disease, winter beans have been displaying high levels of infection that may warrant treatment.

If weather conditions become warm and dry after initial infection, disease development halts and plants produce new and healthy growth.

Treatment with metalaxyl-M as SL 567A will control infection on new growth. Some micronutrient products containing phosphites may allow plants to produce greater defence against downy mildew infection.

Downy mildew in peas
Downy mildew in peas is also present in some crops and the life cycle is the same as disease development in field beans, although the strains of the disease in peas are not thought to be pathogenic in beans.

Downy mildew in peas

In vining peas mandipropamid (Revus) is available to help control downy mildew, but there are no foliar fungicides for downy mildew control in combining peas. Choice of variety helps to reduce disease infection as there are several varieties with good resistance to downy mildew.

Aphids
Pea aphids are now present in some crops, and those crops that are still at early growth stages will be susceptible to virus infection and development. Pirimicarb is approved for control of aphids in both vining and combining peas, but only a single application is permitted and therefore careful consideration must be given to timing of application in combining peas, in which there are no completely effective alternative aphicides. Flonicamid (Teppeki, Afinto, Pekitek) is also approved in vining peas and may be used as an earlier application to help reduce virus infection. Pyrethroids provide only partial control of aphids.

For any information about pest management please contact PGRO at 01780 782585 or becky@pgro.org.